Could Kale Cause Hypothyroidism?

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Recently an online column titled “Kale? Juicing? Trouble Ahead" caught my attention. "Wait a second," I thought, "how could kale, the rising super star of veggies, be trouble?" The author wrote how, after receiving a diagnosis of hypothyroidism, she went home and, naturally, Googled the condition. She found a list of foods to avoid; number one was kale—which she juiced every morning.

I don’t like to jump to conclusions. What came first: the chicken or the egg? Do we know for sure that kale caused her hypothyroidism, or does she simply need to limit her intake because of her diagnosis? Since about everyone I know is on the kale bandwagon these days, let me tell you what I do know for sure.

Kale is a cruciferous vegetable. Cruciferous vegetables are unique in that they are rich sources of sulfur-containing compounds known as glucosinolates. Glucosinolates form a substance called goitrin that can suppress the function of the thyroid gland by interfering with iodine uptake, which can, as a result, cause an enlargement of the thyroid.

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Now, unless you have an iodine deficiency, which is very hard to come by these days (since the 1920s when iodized salt was introduced, deficiency in the U.S. almost completely disappeared), chances are you will not develop a thyroid problem from cruciferous vegetables. The most common cause of hypothyroidism in the U.S. is autoimmune-related, and it is when the body's natural defense system (immune system) makes antibodies that attack and eventually destroy the thyroid gland; this is also known a Hashimoto’s thyroiditis.

However, according to the Oregon State University Micronutrient Information site: “Very high intakes of cruciferous vegetables…have been found to cause hypothyroidism (insufficient thyroid hormone) in animals. There has been one case report of an 88-year-old woman developing severe hypothyroidism and coma following consumption of an estimated 1.0 to 1.5 kg/day of raw bok choy for several months."

Let’s put this into perspective: One kilogram (kg) of kale would be equal to around 15 cups a day. I don’t think even the biggest kale lovers out there are probably consuming that much. And if they are, I wonder at what risk they put themselves for not consuming enough of other nutrients. There has been one study to date on Brussels sprouts (another cruciferous vegetable) that found that consumption of 150 grams (5 ounces) a day for four weeks had no adverse effects on thyroid function. Phew, that’s a relief since I probably do consume around 1 cup a day.

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I think two other things are important to remember here:
1. If you’ve have already received a diagnosis by your physician of hypothyroidism, limiting—not avoiding—raw cruciferous vegetable would be playing it safe. Other cruciferous veggies include bok choy, broccoli, cabbage, cauliflower, collards, turnips, spinach, and mustard greens. The goitens formed can be at least partially destroyed by heat, so consider enjoying these foods cooked rather than raw. If you are a big fan of juicing, keep in mind how many cruciferous veggies overall go into your drink each day.

2. No one food is a superstar. A varied diet is always important. And there are a ton of non-cruciferous, nutritious veggies—string beans, asparagus, lettuce, tomato, mushrooms, peppers—that should also be included in your diet.

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